1. Field of the Invention
The invention relates to a welding structure for a synthetic resin intake manifold in which a synthetic resin passage structural member is welded to a synthetic resin intake manifold body along a joining line that has a loop shape. More specifically, the invention relates to an approach that enables welding to be smoothly performed while ensuring that welding burr does not protrude toward an inside of the joining line when welding.
2. Description of the Related Art
Welding structures for this type of synthetic resin intake manifold are generally known in which a synthetic resin passage structural member that forms at least a portion of a synthetic resin intake manifold is welded along a joining line that has a loop shape to a synthetic resin intake manifold body that forms the rest of synthetic resin intake manifold. Joining flanges are respectively provided on the synthetic resin intake manifold body and the synthetic resin passage forming member along the joining line. A first one of the joining flanges is provided with a protrusion that protrudes towards a second one of the joining flanges. The second joining flange is provided with (i) a welding protrusion which protrudes towards the first joining flange and which is welded to the above mentioned protrusion, and (ii) inside and outside control walls which protrude toward the first joining flange at an inside and an outside of the joining line and which are disposed to either side of the welding protrusion.
However, with the above described welding structure for a synthetic resin intake manifold, when the synthetic resin passage structural member is positioned and aligned with respect to the synthetic resin intake manifold body along the joining line prior to welding, a volume of an inside burr retaining groove formed by the protrusion of the first joining flange and the inside control wall of the of the second joining flange and the welding protrusion of the of the second joining flange, and a volume of an outside burr retaining groove formed by the protrusion of the first joining flange and the outside control wall of the second joining flange and the welding protrusion of the second joining flange are set to substantially the same volume. When the welding protrusion of the second joining flange is welded to the protrusion of the first joining flange and forms welding burr, the welding burr flows to both the inside and outside of the joining line, and is retained in the inside and the outside burr retaining grooves. However, there is a possibility that welding burr that overflows form the inside and outside burr retaining grooves will protrude toward both the inside and outside. If this occurs, it is possible to deal with the welding burr that protrudes toward the outside by removing the protruding portion with a cutter or the like. However, there is no way to treat the welding burr that protrudes toward the inside. Accordingly, the protruding portion will form an obstruction that causes worsening of intake air flow resistance.
To address this problem, technology has been proposed (for example, Japanese Patent Laid-open Publication No. 2002-89388) in which a protrusion of a first joining flange is formed to extend further to an inside than a welding protrusion of a second joining flange. A blocking protrusion is formed at an inside end of the extended protrusion in order to block welding burr that is going to overflow from the inside burr retaining groove at the outside of the inside control wall of the second joining flange (namely, the inside of the inside burr retaining groove). Accordingly, protrusion of welding burr toward the inside from the inside burr retaining groove can be regulated.
However, in the technology, there is a possibility that, when the inside burr retaining groove becomes full of welding burr, the welding burr will pass over the extended protrusion and protrude toward the inside. Moreover, on the other hand, if the welding burr does not pass over the extended protrusion after the welding burr has filled the inside burr retaining groove, the welding burr has no place to escape to at the inside. As a result, there is a possibility that welding of the synthetic resin passage structural member to the synthetic resin intake manifold body will not be performed smoothly and that bulging will occur at an inside portion of the joining line where the joining flanges are welded together. Accordingly, in the technology, it is not possible to address the problem of the welding burr protruding to the inside when the synthetic resin passage structural member is welded to the synthetic resin intake manifold body.